US1985166A - Method of making electric resistance - Google Patents

Description

Dec. 18, 1934. A. HAROLDSON 1,985,166

METHOD OF MAKING ELECTRIC RESISTANCE Filed May 1, 1950 Patented Dec. 18, 1934 PATENT OFFICE METHOD or MAKING mo'mro aasrs'ranon Haroidson, Valparaiso, Ind assigno'r, by means assignments, to Continental Diamond :3? Company, Newark, Dei., a corporation a iiumion May 1, mo, Serial No. 448,900 0m (01. sol-'11s) My present invention relates in general to electrical conductor material particularly adapted for use in electrical resistance units.

The invention is particularly adapted for the 5 production of volume controls or fixed resistors particularly adaptable for radio apparatus where inexpensive but,accurate control of electrical cir-.'

cuits is important. The invention is also adapted for use in precision rheostats and other resistance units used in electric circuits.

One of the objects of my invention resides in providing a method for making resistors wherein the measuring of predetermined quantities of the conductive substance of which the unit is 16 composed is accomplished in a simple and inexpensive manner, and wherein the same in its molded state is consolidated with a relatively thin base or carrier formed by means of a heat curable material. 7

Yet another object of my invention resides in the provision of a resistance unit made by the method herein disclosed.

These andother objects of my invention will be apparent from a perusal of the following speci- 26 fication when taken in connection with the accompanying drawing wherein:

Figure 1 is a bottom view of one form of die by means of which the shape and amount of conductive material may be applied directly to either 30 a sheet of treated or untreated material;

Figure 2 is a perspective view showing a sheet of tissue paper impressed by the die shown in Fi ure 1; 1

Figure 3 is a view showing said strip of tissue 36 paper superimposed upon a sheet of heat curable material in its unreacted state;

1 Figure 4 is a view of the laminated finished material provided with a number of the resistance units:

I 9, Figure 5'is a view similar to Figure 3 showing a manner in which the conductive materials are pressed by a die directly on a sheet of untreated thermo-plastic material but before the latteris heated and pressed to finished form;

Figure 6 is a perspective view of a resistor which is provided with a graduated carbon deposition made in accordance with my invention; and

Figure 7 is a side view of the same. In my improved method for forming a resist- 50 ance unit, I provide a die preferably of metal provided with one or more cavities of desired shape and cross section and adapted to contain a predetermined and measured amount of conductive material.

, In the present instance, the die is illustrated as showing one or more impressions or cavities so that when impressed upon a sheet of material it will form simultaneously one or more shapes thereon, all of which are identical and each forming on the material impressed, a single or a se- 5 ries of units, each containing a measured or predetermined amount of such conductive material.

The conductive composition may include any type of conductive material such as graphite, car 10 bon, aluminum, copper and the like, in finely divided form. I prefer to use graphite or carbon, preferably in the colloidal form. In the present instance I use colloidal graphite which is known among the trade as "Aquadag. I may also form a suspension of graphite or carbon in amyl acetate or the conductor material may be formed as a water suspension in gelatin, together with a trace of ammonia as a binder for the powdered conductor so asto assist the finely divided conductive material in retaining a substantially moldable form for impressiori'or deposition upon the carrier.

Instead oi making single or multiple impressions from the die, I may provide a die of continuous and cylindrical construction to operate either continuously orperiodically upon a strip or sheet of material fed in proximity to the die so that a continuous process may be afforded. The die is provided with means for intermittently or con-, tinuously filling the impressions with conductive material and for scraping off the surplus material so that each cavity will contain the same amount 01 conductive material. This die is rotated or positioned so as to successively deposit upon the periodically fed strip, a succession of such deposits.

Inany case, in using either a single die or a rotary die, after the cavity in the die has been filled with the conductive material, the surplus must be scraped off so as to have only a precise amount of material in the cavity whereby uniformity and accuracy in measurement is secured .for each of the die impressions.

In another aspect of my invention, the conducting material itself may be mixed with an insulating material in various proportions in order to vary the conductivity and resistance per unit length in the resulting material. By properlycontrolling the ratio of conducting to nonconducting material during manufacture, a material is maintained having any desired resistance and conductive characteristics. However, in the present instance, the resistance unit is disclosed 8, be ng Iormed of the conductive substance such as graphite or carbon without being admixed with a filler or insulating material.

In each instance, this conducting material will adhere to the cavities of the. die, but when the die is impressed to the sheet material, the conductive. material will pull away from the die and adhere to the sheet, due to the natural adhesive qualities of the paper or greater adhesive attraction between the substance and paper than between the substance and the metal die.

In this way, the measured amount of COD-7' ductive material of the desired cross section and of the desired resistance is applied directly to the sheet material or carrier, such as absorbent fibre paper of 5 mils in thickness, or upontissue paper, either of which may be treated or untreated with heat curable material inits unreacted state. In the preferred manner of carrying out my invention, the die 2 carrying the one or more cavities i ls impressed directly upon the carrier strip, or sheetof thin paper, such as tissue-paper 6, thereby leaving thereon the corresponding measured amounts of conductive ma terial 8 of the desired cross sectional shape and configuration. After this has been done, the carrier strip or sheet of thin paper carrying the strip of depositions is superimposed upon a base 10 comprising a resin treated sheet or sheets of paper or fabric.

The sheet and base are then inserted in the usual press and subjected to heat and pressure whereby the tissue paper carrier and the base will be consolidated and permanently and integraliyunited. During the molding process, the heat curable resin will permeate the carrier strip and the deposited resistor units so that in this manner, a cured strip of Bakelite will be formed having consolidated and molded in the surface thereof a series of resistance units, each unit being of desired cross sectional shape and electrical characteristic. The separate units may then be cut out and used in any desired manner.

Instead of depositing the resistor units on the carrier sheet of tissue paper, I may apply them directly to the base as shown in Figure 5 of the drawing, in which case the carrier sheet of tissue paper is dispensed with and the resistance units will be directly and integrally consolidated with the base during the heat treating and pressing operation.

In some instances I may die press the conductive units to an untreated sheet to which a thermo-plastic resin can afterwards be applied, or alternatively, this untreated sheet may be superimposed on a Bakelite or resin-treated sheet so that the Bakelite of the second sheet will penetrate the first sheet and bind them together to provide a laminated base or carrier to which the units are consolidated. In either case the sheets will then be treated with heat and pressure to consolidate the units to the sheet or sheets.

It is to be understood that when I refer to sheets which are to be treated with "BakeI-ite or other resin compound, I include not only paper sheets, but also fabric sheets.

In certain instances, as shown in Figures 6 and 7, my invention comprehends the production of electric resistance material or a resistor wherein the resistance is controlled by the thickness of the graphite or carbon deposited. For instance, in certain portions of the resistor, the graphite or carbon is deposited relatively thick and as the resistance tapers off, the thickness of the deposition gradually decreases. Referring to Figures 6 and 7,. the same show a resistor or other element made in accordance with my invention comprising the base or carrier 10 of resin treated sheet material with the resistor consolidated therewith in accordance with the method hereinbefore set forth. In this instance, the carbon, graphite, or other deposition 12- is of tapering or graduated thickness, the end of the resistor at the left shown in Figures 6 and 7 being thicker with the deposition gradually thinning toward the right, or toward the other end of the resistance element.-

In the same manner, my invention contemplates the provision of a resistor having different zones of its surface provided with cross sectional areas of conducting material of different thicknesses. This is of course controlled by the depth of the die cavity when the same is deposited upon 'the sheet material, as hereinbefore described.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

l. The herein described method of forming units of the character described which includes pre-forming a measured amount of a'conductive substance to a desired form and cross section, impressing the same upon'a very thin sheet in such a manner that the unit in its formed shape adheres directly to said sheet, applying said sheet to a second sheet and consolidating said unit,-

said first sheet and said second sheet, by means of a resinous binder through the action of heat and pressure.

2. The herein described method of forming an electric unit of the character described which consists of molding a measured amount of electrically conductive material to desired shape and cross section, impressing the same directly upon a sheet of tissue paper, applying the sheet of tissue paper to a sheet of material treated with phenolic condensation product and applying heat and pressure thereto.

3. The herein described method of forming an electric unit which consists in filling the cavity of a die of predetermined shape and cross section with a moldable electrically conductive material, passing a scraping instrument over the surface of the die to remove surplus material and thereby leaving a measured amount of said material in the die, impressing the die upon a sheet and superimposing said sheet upon a second sheet and consolidating said two sheets and said substance permanently by means of a resinous binder and under heat and pressure.

4. The process of making resistance units which includes the steps of causing an adherence of a preformed mass of moist particles of resistance material having predetermined resistance characteristics to an absorbent carrier sheet to provide a combined unit having predetermined resistance characteristics, and embedding the combined unit under heat and pressure in a base impregnated with an uncured phenol condensation product.

5. The process of making resistance units which includes the steps of preforming a quantity of conductive material to a desired form, im-

pressing the same upon an absorbent carrier to cause adherence of the conductive material to said carrier, applying said carrier to a second carrier, and consolidating the composite struc-

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